This invention relates to a resin composition for coating and a paint containing the resin composition.
A paint to be used to mortar, slate or concrete for building facing is required to have high durability such as weather resistance, water resistance, moisture proof, alkali resistance and acid resistance. A paint using a copolymer mainly comprising an acrylate and a methacrylate which is so-called a solvent type acrylic resin as a vehicle has been used for building facing since it is excellent in coating workability and in durability. There is, however, a problem of toxicity to a human body or pollution to environment, since a thinner mainly comprising toluene and xylene is used for coating with a large amount. Also, when the paint is used for repairing an outer coating film, toluene and xylene which have higher dissolving power and contained in the paint violate the outer coating film to cause a lifting phenomenon so that such a paint can be difficultly used for repair. On the other hand, as a paint in which the problems of repairing property or toxic property to human body or environment have solved, there is a paint using an acrylic emulsion resin which uses water as a medium. However, it is inferior in durability as a coating for building facing, particularly in water resistance and moisture proof so that it cannot be practically used.
As a resin having intermediate characteristics between the above solvent type acrylic resin and the acrylic emulsion resin, there is a non-aqueous dispersion type acrylic resin. The non-aqueous dispersion type acrylic resins use an aliphatic hydrocarbon or a solvent mainly comprising an aliphatic hydrocarbon as a solvent so that toxicity to human body or environment is small as compared to that of the conventional solvent type acrylic resins. Also, an emulsifier having a strong hydrophilic property is not contained therein so that durability is also good. Whereas the non-aqueous dispersion type acrylic resin has such characteristics, weather resistance is insufficient as compared to those of the solvent type acryl-urethane paint or a fluorine resin, and improvements in characteristics have been desired.
On the other hand, a silicone resin is excellent in heat resistance and weather resistance, and a silicone-modified acrylic resin which is utilized the characteristics of the silicone resin has been tried to use as a paint. In Japanese Patent Publication No. 443/1988 (which corresponds to U.S. Pat. No. 4,334,036), there is disclosed a process of hydrolyzing and condensing a solvent type acrylic resin having a silyl group in the presence of a curing catalyst. A coating film obtained by the process is excellent in chemical resistance and water resistance but mechanical strength thereof is not necessarily sufficient and there are also defects of poor stain resistance or poor coating workability. Also, in Japanese Provisional Patent Publication No. 116605/1987 (which corresponds to U.S. Pat. No. 4,965,312), there is disclosed a process for preparing a non-aqueous dispersion type acrylic resin by polymerizing an acrylate(s) and a methacrylate(s) in the presence of a polysiloxane resin. In this method, a non-aqueous dispersion can be obtained but film forming property is insufficient. Further, in Japanese Provisional Patent Publications No. 75502/1989 and No. 95116/1989 (which correspond to EP-A-0 308 203), there is disclosed a composition in which a curing catalyst is formulated to a non-aqueous dispersion using an acrylic resin having a silyl group as a dispersion stabilizer or dispersant. These compositions are excellent in mechanical strength and chemical resistance of a coating film but stain resistance or storage stability is not necessarily sufficient. Furthermore, in Japanese Provisional Patent Publication No. 64110/1990, there is disclosed a non-aqueous dispersion type composition using a vinyl type polymer having a hydrolizable silyl group as a dispersion resin particle, but the composition is inferior in stain resistance or coating film hardness.